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Nature of Science

Performance Benchmark N.8.A.4
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Nature of Science
Scientific Inquiry




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Nature of Science (NOS)
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Students know how to design and conduct a controlled experiment E/L

Scientific inquiry is defined in the National Science Education Standards (NSES p.23) as “the diverse ways in which scientists study the natural world and propose explanations based on the evidence derived from their work.  Scientific inquiry also refers to the activities through which students develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world.”  Middle school students should develop their ability to do inquiry in science classes.  As part of inquiry learning, students should be encouraged to ask questions and design investigations to attempt to answer the questions.  However, to be taught to think and work scientifically, they need to learn how to identify questions that can be studied scientifically, to design a study so that the most accurate observations can be made, and then to use evidence from that study to support conclusions.  Learning how to design and conduct controlled experiments is a valuable academic tool to help students develop their inquiry skills. 

 There are many ways to “do” science.  Scientists learn from observing, asking questions, using models, and by gathering information, data, and evidence from various sources.  All of these methods of science are valuable and students should experience a variety of ways of doing science.  When a scientist wants to test a specific concept or the effect of a specific variable, using a laboratory or other physical setting, he/she will often design and execute a controlled experimentA controlled experiment is one that generally will compare an experimental sample to a control sample.  Both experiments are identical except for one “variable” that is changed or tested in the experimental sample.  For example, if you wanted to see if a plant grew as well in the dark as it did in the light, you could conduct a controlled experiment that includes growing plants in the dark, and growing plants in the light.  To be sure that the light was the only thing that affects the outcome, everything else such as temperature, type and amount of soil,  and the amount of water given has to be exactly the same for both groups.  Traditionally, students learn about the “Scientific Method” when being taught about controlled experiments.  The scientific method, although not always used by scientists, is often included as a fundamental method in textbooks and taught by many teachers as a way to teach about controlled experiments.  Teaching students the scientific method is useful because it helps young minds to learn the importance of reasoning and developing systematic ways to solve a problem or answer a question.  It also provides a foundation for learning how to conduct a controlled experiment, and helps students organize and plan a scientific study to answer questions about the natural world.    

Students however, must also learn that not all science follows the specific, detailed, step-by-step process that is called the scientific method.  “The scientific method” is not the only scientific method.  Discoveries are made through observations, trial and error, development and use of models, and various other processes and all of these processes must be encouraged. 

For further information related to scientific investigations and inquiry see
MS TIPS Benchmark N.8.A.6.

Students need to be challenged to investigate and analyze questions about nature.  This requires encouraging them to independently develop tests and experiments on their own, rather than providing them with “cook book” scientific verification labs.  They need to learn how to use evidence to support an answer or an explanation.  They need to learn how to record and evaluate data and results.  Through teaching how to design and conduct controlled experiments, students learn how to identify variables and how to control all the variables in an experiment.  Teaching all of these scientific processes and more can be facilitated by incorporating the scientific method.  We will therefore look at steps generally included in lessons about the scientific method and controlled experiments.  These steps, although not necessarily completed in this specific order, are: observing, questioning, researching and more observing, hypothesizing, experimenting, analyzing, communicating, and questioning further.  The scientific method can more accurately be called an “Inquiry Cycle.”

Figure 1. Cyclic nature of scientific investigations.


To read more about how controlled experiments and the scientific method are incorporated into scientific research, see .

Controlled Experiments
A controlled experiment is one that generally will compare an experimental sample to a control sample.  Both experiments are identical except for one “variable” that is changed or tested in the experimental sample.  For example, if you wanted to see if a plant grew as well in the dark as it did in the light, you would run two tests…one with plants in the dark, and the other with plants in the light.  Everything else such as temperature and the amount of water given has to be exactly the same for both groups. 

Several studies completed by scientists to debunk the idea of abiogenesis provide good examples of controlled experiments and their benefit of supporting scientific hypothesis and testing theories.  Aristotle believed life came from non life.  Beginning in the 1600’s, several studies ultimately led to the rejection of this theory of spontaneous generation.  Francesco Redi used controlled experiments to disprove spontaneous generation.  The figure below illustrates his controlled experiment.  The only difference between the experimental samples was whether or not flies could directly access the meat.  His conclusion was that maggots do not spontaneously appear out of meat, but rather they come from flies.

Redie's Fly <a href=Experiment">

Figure 2. Redi’s controlled experiment illustration.

Other scientists conducted controlled experiments that supported the hypothesis that life only comes from other life and does not spontaneously appear,  Pasteur’s (1800’s) experiments  provided strong evidence that life arose from other life.  In this classic experiment, all conditions were the same for all flasks used, except for the exposure to particles in the air. 

Figure 3. Illustration representing Pasteur’s study was retrieved.


To read more about the scientific studies disproving spontaneous generation see

These and other experiments were early examples of controlled experiments.  They were repeated many times, and only one variable was altered.

Let’s look now at specific steps used to design and implement a controlled experiment.  There are many resources in text books and on line that discuss the various steps of the scientific method, which as discussed earlier is not the only method of science, but does serve as a tool  that can be used to teach about controlled experiments.

Designing a Controlled Experiment Requires Identifying a Problem or a Question
By observing the natural world, students can identify questions.  In order for a question to be studied in a controlled experiment, it needs to be something that can be tested scientifically.  It should be specific and limited.  It should also be open ended, and not able to be answered with a simple yes or no.

For further discussion of a Problem visit

Hypothesis is Identified Before an Experiment is Designed
Prediction can be used as a hypothesis.  Some texts define a hypothesis as an “educated guess”.  While this is partially true, we have to be careful to teach students that it is much more than a guess.  Rather, a hypothesis is a possible answer to the question, and is based on what is known or understood.  A scientific hypothesis should be testable, measurable, specific, and clearly understood. 

To learn more about what a hypothesis is or should be, see

Experimental results may either support or not support a hypothesis.  When results do not support a hypothesis, the hypothesis should not be called “wrong.”  Instead, it can be said that the hypothesis is not supported based on evidence.  When that occurs, the hypothesis could be reformulated based on observations and another controlled experiment to test the new hypothesis could be designed.  A theory is a hypothesis that is supported after many tests. 

Plan a Controlled Experiment
Designing a controlled experiment takes practice and time.  The experiment must be replicable, have sufficient sample sizes, and needs to be designed so that only the variable being tested varies.  A reliable acceptable controlled experiment is sometimes called a “Fair test” which is one in which only one factor at a time is changed while all other conditions are kept constant.  When designing a controlled experiment, step-by-step procedures should be written, all variables need to be clearly identified, and a method of gathering data should be developed. 

For additional information on fair tests see


Many science fair related sites provide explanations and examples of the scientific method and often times science fair organizers prefer the “traditional” scientific method as a standardized format for entries. 

To learn more about science fair and science fair projects visit
Discovery Education
Science at
Science Buddies at

To learn more about how to choose and use appropriate laboratory equipment and tools refer to MS TIPS Benchmark N.8.A.5

Controls and Variables
A crucial part of designing a controlled experiment is to identify the variable to be tested and the controls needed to assure that results are due to the variable being tested and not other conditions or influences. 

Variable is the treatment or condition that is to be tested.  In a controlled experiment, the variable is the only thing that should be different between different experimental set ups.  Some texts describe both the independent and dependent variable, but it is not necessary to teach middle school students that vocabulary.  The important thing to help these students is to help them learn that in a controlled experiment, only one variable is to be tested, and that everything else in the experiment should remain constant.

Controls are conditions and treatments in a controlled experiment that are kept constant.  To determine if that variable affects the outcome of the experiment, a control must also be run which entails the exact same conditions, but without the variable being tested.  For example, if we wanted to test the effect of salt water on the growth of plant X, you would water (several samples) of plant X with the same concentration of salt water.  The concentration of the salt would remain the same throughout the experiment as would other conditions such as the amount of water, light, temperature, etc.  The control would be to run the same experiment using no salt in the water, but keeping everything else the same. 

The following chart provides examples of variables and controls.  Although middle school students do not need to learn the terms Independent Variable and Dependent Variable, the following table illustrates examples of variables and controls. 


Independent Variable
(What I change)

Dependent Variables
(What I observe)

Controlled Variables
(What I keep the same)

How much water flows through a faucet at different openings? 

Water faucet opening (closed, half open, fully open)

Amount of water flowing measured in liters per minute

The Faucet

Water pressure, or how much the water is "pushing"

"Different water pressure might also cause different amounts of water to flow and different faucets may behave differently, so to insure a fair test I want to keep the water pressure and the faucet the same for each faucet opening that I test."

Does heating a cup of water allow it to dissolve more sugar? 

Temperature of the water measured in degrees Centigrade

Amount of sugar that dissolves completely measured in grams


Type of sugar

"More stirring might also increase the amount of sugar that dissolves and different sugars might dissolve in different amounts, so to insure a fair test I want to keep these variables the same for each cup of water."

Does fertilizer make a plant grow bigger?

Amount of fertilizer measured in grams

Growth of the plant measured by its height

Growth of the plant measured by the number of leaves

See Measuring Plant Growth for more ways to measure plant growth

Same size pot for each plant

Same type of plant in each pot

Same type and amount of soil in each pot

Same amount of water and light

Make measurements of growth for each plant at the same time

"The many variables above can each change how fast a plant grows, so to insure a fair test of the fertilizer, each of them must be kept the same for every pot."

Does an electric motor turn faster if you increase the voltage?

Voltage of the electricity measured in volts

Speed of rotation measured in revolutions per minute (RPMs)

Same motor for every test

The motor should be doing the same work for each test (turning the same wheel, propeller or whatever)

"The work that a motor performs has a big impact on its speed, so to insure a fair test I must keep that variable the same."

Table 1. Examples of Variables and Controls

For additional information on controls, see

Once the decision has been made as to what to test, and an experimental procedure has been developed, the following table from Science can be used as a check list for the experimental design:

What Makes a Good Experimental Procedure?

For a Good Experimental Procedure, You Should Answer "Yes" to Every Question

Have you included a description and size for all experimental and control groups?

Yes / No

Have you included a step-by-step list of all procedures?

Yes / No

Have you described how to the change independent variable and how to measure that change?

Yes / No

Have you explained how to measure the resulting change in the dependent variable or variables?

Yes / No

Have you explained how the controlled variables will be maintained at a constant value?

Yes / No

Have you specified how many times you intend to repeat the experiment (should be at least three times), and is that number of repetitions sufficient to give you reliable data?

Yes / No

The ultimate test: Can another individual duplicate the experiment based on the experimental procedure you have written?

Yes / No

If you are doing an engineering or programming project, have you completed several preliminary designs?

Yes / No

Table 2. Procedure checklist.

To learn more about designing a fair experiment, see

Data must be collected and recorded appropriately
As the controlled experiment is being conducted, data must be gathered and recorded in an organized and thoughtful way.  The data may include measurable (quantitative) and descriptive (qualitative) observations.  Tables, charts, and illustrations should be labeled completely and clearly.  Data gathered in an experiment should be organized and clear.  The following three slides are from a PowerPoint online.  They illustrate the difference between good data recording and poor data recording.

Figure 4. Poorly organized data.

Figure 5. Unlabeled data.


Figure 6. Clear and organized data.

Other examples of data presentation can be found at

Generally, students should gather quantitative data in a table format, which can then be later graphed or charted.

For information on how to evaluate information in tables, graphs, and charts see
MS TIPS Benchmark N.8.A.1

For additional ways of organizing information see MS TIPS Benchmark N.8.A.7 

In addition, to learn more about presentation of data in charts, tables, graphs and diagrams, see

Two types of data can be recorded during an experiment: Quantitative and Qualitative

Quantitative Data is measurable and can be recorded numerically.  Examples would be height, weight, length, time, and other measurements that can be recorded as or associated with a number. 

Qualitative Data is not specifically measurable by numbers, but is recorded as descriptions or choices, or other observations that are not easily associated with numbers.  Qualitative data could include things such as a description of the way a plant looks as it grows.  The following table presents distinctions between qualitative and quantitative data. 



"All research ultimately has
a qualitative grounding"
- Donald Campbell

"There's no such thing as qualitative data.
Everything is either 1 or 0"
- Fred Kerlinger

The aim is a complete, detailed description.

The aim is to classify features, count them, and construct statistical models in an attempt to explain what is observed.

Researcher may only know roughly in advance what he/she is looking for.

Researcher knows clearly in advance what he/she is looking for.

Recommended during earlier phases of research projects.

Recommended during latter phases of research projects.

The design emerges as the study unfolds.

All aspects of the study are carefully designed before data is collected.

Researcher is the data gathering instrument.

Researcher uses tools, such as questionnaires or equipment to collect numerical data.

Data is in the form of words, pictures or objects.

Data is in the form of numbers and statistics.

Subjective - individuals’ interpretation of events is important ,e.g., uses participant observation, in-depth interviews etc.

Objective – seeks precise measurement & analysis of target concepts, e.g., uses surveys, questionnaires etc.

Qualitative data is more 'rich', time consuming, and less able to be generalized. 

Quantitative data is more efficient, able to test hypotheses, but may miss contextual detail.

Researcher tends to become subjectively immersed in the subject matter.

Researcher tends to remain objectively separated from the subject matter.

Table 3. Qualitative v. Quantitative Data.
 (The two quotes are from Miles & Huberman (1994, p. 40). Qualitative Data Analysis)

Conclusions Must be Supported by the Evidence Gathered
Experimental evidence, data and observations, are what validate a hypothesis.  Evidence makes science valid or confirmed.  Much evidence is needed to validate a hypothesis.  If only one plant is treated with fertilizer, and one plant is treated with no fertilizer, and the fertilizer plant dies, a conclusion could be that fertilizer does not help a plant grow.  However, if only one plant is tested—what if that plant was diseased or had some problem before it started in the experiment?  A scientist would have to test MANY plants.  Say for example if 50 plants were treated with fertilizer and all of them except for one grew taller than those without fertilizer, one could have confidence stating a conclusion that the fertilizer makes the plants grow taller.  The one that did not grow could have been a faulty plant.

For discussions as to how data and evidence can be interpreted differently or used to explain results in more than one way visit MS TIPS Benchmark N.8.A.3

From results, and based on evidence, an inference can be made.  An inference is a conclusion based only on what is observed or learned during the scientific experiment.  A conclusion is a tentative answer to the original question.  This conclusion should either support or not support the hypothesis and must be based on evidence gathered in the experiment.  Any data, observations, or evidence used to support a conclusion must be based on fact and not opinion.   

To learn more about how to evaluate information to distinguish between fact and opinion visit MS TIPS Benchmark N.8.A.2

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Performance Benchmark N.8.A.4

Students know how to design and conduct a controlled experiment E/L

Common misconceptions associated with this benchmark

1. Some students think that “The Scientific Method” is the only correct way to do science investigations.

This is a danger of teaching the scientific method.  It is important to teach students inquiry as a process, and use scientific method as ONE of many tools in the science classroom.  “The Scientific Method” is sometimes used by scientists to test hypothesis.  It is taught in many classes, described online, and can be a useful tool to teach young scientists.  However, a teacher needs to be careful not to mislead students into believing that this is the only method of science.  Science fair projects and scientific publications can contribute to an ongoing perpetuation of this misconception, because this is the way that scientific studies are often presented.  In reality there is no one set method that scientists use universally.  Scientists approach solving problems with perseverance, creativity, prior knowledge, and repeated testing. 

Some examples of experiments including controlled experiments as well as others can be read at

2. Middle school students may think experiments are a way to produce a desired outcome, rather than a way of testing ideas.

Students are often given “cookbook” type experiments where the steps are already written for them and controls are already identified.  If the experiment does not turn out the expected way, students think they did something wrong.  Therefore, it is necessary that students are given many opportunities to design their own experiments and defend their conclusions with evidence acquired.  As students experience more inquiry-based activities and labs, they will develop inquiry skills as well as the ability to identify controls, errors, and successes in experimental designs. Inquiry can be encouraged by sometimes modifying standard text book verification labs.  

To learn how to convert standard labs into more inquiry-based experiences, see the following two resources

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Performance Benchmark N.8.A.4

Students know how to design and conduct a controlled experiment E/L

Sample Test Questions

1st Item Specification: Given a specific question, design a way to test the question using appropriate variables and controls, defend the use of experimental design, and describe weaknesses or flaws in the test, experiment, or research design.

Depth of Knowledge Level 1

  1. Which question could be used to conduct a scientific experiment?
    1. What is the most popular radio station?
    2. How does high Definition TV work?
    3. Why do I get headaches in school and at home?
    4. Does the color of light affect the growth rate of plants?
  1. A scientific investigation is designed to test the effects of salt on the freezing point of water. What is the control group for this investigation?
    1. Tap water with nothing added to it.
    2. Tap water with 1 cup of salt added to it.
    3. Ocean water with 1 cup of salt added to it.
    4. Ocean water with nothing added to it.

Depth of Knowledge Level 2

  1. Consider the question, “Does cold water freeze faster than hot water?”
    What is the BEST way to setup an experiment to test this question?
    1. Ask a friend to put one tray of hot water and one tray of cold water into his freezer. Have him record the temperatures of the two trays every 45 minutes, until both trays have froze solid.
    2. Ask three neighbors to put one tray of hot water and one tray of cold water in their freezer. Have them record the temperatures of the two trays every 45 minutes, until both trays have froze solid.
    3. Put one tray of hot water into your freezer and record the temperature of the tray every 45 minutes, until the tray has froze solid. Then put one tray of cold water into the same freezer and record the temperature of the tray every 45 minutes, until the tray has froze solid. Repeat this procedure three times.
    4. Put two identical trays filled with equal amounts of water, one with hot water and one with cold water in your freezer. Check on the trays every 45 minutes to see which one freezes solid first.
  1. Identify the flaw in the following experiment.  A student asked three friends to put some trays in their freezers, some would have hot water and some would have cold water. They would then time how long it takes for each tray to freeze solid, and then call him to give their results.
    1. There are too many variables that could affect the results of the test.
    2. There were no time limits given to complete the test.
    3. There is no benefit to this test.
    4. There will be no quantitative data to collect by the students.

2nd Item Specification: Given an example, identify which variable(s) should be controlled in the experimental design.

Depth of Knowledge Level 1

  1. Which of the following is the independent variable given the hypothesis; “Does the concentration of salt in water effect the rate at which it freezes?”
    1. Temperature
    2. Time
    3. Concentration of salt
    4. Type of container
  1. Which of the following is the dependent variable given the hypothesis; “Does the concentration of salt in water effect the rate at which it freezes?”
    1. Temperature
    2. Time
    3. Concentration of salt
    4. Type of container
  1. Which of the following is the BEST variable to control when testing the hypothesis; “Does the concentration of salt in water effect the rate at which it freezes?”
    1. Temperature
    2. Time
    3. Concentration of salt
    4. Type of containers

Depth of Knowledge Level 2

  1. A student was asked to design an experiment to test the effects the color of light has on the growth rate of plants. When planning to conduct this experiment, which of the following is the BEST list of variables that should be controlled?
    1. Type of plants, amount of soil, amount of light, color of light, growth rate of the plants
    2. Type of plants, amount of light, amount of water, color of light, final number of leaves on the plants
    3. Amount of soil, color of light, type of plants, amount of water, amount of light
    4. The color of light, the growth rate of plants, the final number of leaves on the plants, the amount of soil
  1. Which of the following list BEST describes what variables should be controlled when testing the hypothesis; “Does the concentration of salt in water effect the rate at which it freezes?”
    1. Temperature of the freezer, amount of salt added to each container, amount of water in each container, total amount of time the containers are in the freezer before they freeze
    2. Type of containers used, temperature of the freezer, amount of water in each container, total amount of time the containers are in the freezer before they freeze
    3. Temperature of each solution to be tested, the type of containers used, amount of water in each container, the volume of water in each container
    4. Temperature of the freezer, the type of containers used, amount of water in each container, the volume water in each container

3rd Item Specification: Use appropriate vocab when designing and conducting a controlled experiment (qualitative and quantitative, observations, inference, benefit, consequence, inferring, predicting, data, problem, hypothesis, conclusion, control, variable)

Depth of Knowledge Level 1

  1. The part of the experimental design that does not change from setup to setup is called the
    1. control.
    2. variable.
    3. constant.
    4. hypothesis.
  1. Any factor that can change DURING an experiment is a
    1. data table.
    2. control.
    3. hypothesis.
    4. variable.
  1. Which of the following is a quantitative observation?
    1. The bag contains five rocks.
    2. The bag contains pretty rocks.
    3. The bag is heavy.
    4. The bag smells bad.
  1. After conducting an experiment a student is left with several containers of used chemicals, these containers would best be described as
    1. controls.
    2. variables.
    3. a consequence of the experiment.
    4. a benefit of the experiment.

4th Item Specification: Understand how to report data and share findings.

Depth of Knowledge Level 1

  1. After analyzing data a scientist
    1. adds a control group.
    2. makes a conclusion.
    3. stops the experiment.
    4. adds a dependent variable.
  1. During an experiment that requires the collection of large quantities of numbers, these numbers would BEST be recorded in
    1. a data table.
    2. a graph.
    3. the final report.
    4. the hypothesis.
  1. After conducting an experiment and making a conclusion, the next MOST LIKELY step would be to
    1. construct a data table and graph.
    2. think of a hypothesis.
    3. report the findings.
    4. design a new experiment.

Depth of Knowledge Level 2

  1.  When reporting the results of an experiment that collected large quantities of numerical data on the effects of colored light on the growth rate of plants, which of the following would be the BEST way to report the information?
    1. Data tables for each plant.
    2. Individual line graphs for each plant.
    3. A line graph for each color of light used.
    4. Data tables for each all colors of light used.

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Performance Benchmark N.8.A.4

Students know how to design and conduct a controlled experiment E/L

Answers to Sample Test Questions

  1. D, DOK Level 1
  2. A, DOK Level 1
  3. D, DOK Level 2
  4. A, DOK Level 2
  5. C, DOK Level 1
  6. B, DOK Level 1
  7. D, DOK Level 1
  8. C, DOK Level 2
  9. C, DOK Level 2
  10. A, DOK Level 1
  11. D, DOK Level 1
  12. A, DOK Level 1
  13. C, DOK Level 1
  14. B, DOK Level 1
  15. A, DOK Level 1
  16. C, DOK Level 1
  17. C, DOK Level 2

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Performance Benchmark N.8.A.4

Students know how to design and conduct a controlled experiment E/L

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Spontaneous Generation from Science NetLinks

A lesson that demonstrates that scientific knowledge is stable, but also prone to change.  This takes students through the historical scientific studies that led to refutation of spontaneous generation.

To access this lesson visit

2. Scientific Method – A mini lab from Time for Kids

This mini lesson uses a news article to help students learn how to identify problems and write hypotheses.
To access this lesson, visit,28171,1658109,00.html

3. Biology4 Kids Quiz:  The Scientific Method

An online quiz regarding various parts of a scientific method.  Students can take the quiz online and receive immediate feedback on each question.  This quiz can be completed by individual students, or projected and used with the whole class.

To access this online quiz, visit

4. Science Fair Central:  A Soup to Nuts Handbook

This site is designed as a resource for science fair projects.  Whether or not a teacher has students participating in a science fair, this site provides excellent explanations that teachers can use when teaching science processes. 

To access this site, visit

5. Independent Investigation – a graphic organizer

For a simple worksheet that can be used to help students design an experiment, visit

6. How Scientists Work:  The Scientific Method  

This site from, provides a series of short videos that provide examples of scientific method and controlled study steps.  These are all short clips that can be used as examples in the class.  There are short commercials before some of the clips.  Click on the “Related Videos” tab to access all of the video clips.

To access the video clips, visit


7. Experimental Design from Study Stack

This site has various games and game-like activities that can be used to reinforce the vocabulary associated with controlled studies. This site includes matching, hangman, crossword, flashcards, and more.  Some of the vocabulary may be beyond the scope of middle school science, but the students will enjoy the games as they learn!

To access the games, visit


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Benchmark Related Vocabulary